Methods and apparatus for transmitting information between a basestation and multiple mobile stations

ABSTRACT

Methods and apparatus for scheduling mobile stations (MSs) to download data to and/or to control the rate of downloading to an MS from a base station (BS) as a function of downlink channel condition information are described. Artificial channel variations, which can be measured at the MS, and feedback to a BS for scheduling purposes, are introduced through the use of two or more transmitter antennas at a BS. Each of the antennas transmits a signal at the same frequency having the same information content, e.g., modulated data. However the signals are made to differ with time in their phase and/or amplitude. Multiple signals having the same transmission frequency and information content are received and interpreted as a single composite signal by a receiving MS. The interaction of the received signals and the intentional variations introduced into the signals result an MS detecting different signal amplitudes and/or phases over time even when the total amount of power used to transmit the combination of the signals having the same information content remains constant with time. Data transmission rates are controlled in some embodiments as a function of channel conditions, e.g., the better the channel conditions the faster the transmission data rate used. By varying the data rate as a function of channel conditions and by preferring MSs with good channel conditions to those with bad channel conditions, improved overall throughput can be achieved by a BS with regard to downlinks as compared to known systems.

RELATED APPLICATIONS

[0001] The present application claims the benefit of U.S. ProvisionalPatent Application Serial No. 60/232,928, filed Sep. 15, 2000.

FIELD OF THE INVENTION

[0002] The present invention relates to communications systems and, moreparticularly, to methods and apparatus for communicating between basestations and mobile stations.

BACKGROUND OF THE INVENTION

[0003] Several technologies are competing to provide wireless dataand/or voice service. Competing technologies include the ThirdGeneration (3G) wireless standard which uses Code Division MultipleAccess (CDMA); High Data Rate (HDR) by Qualcomm; and Flash-OFDM byFlarion Technologies the assignee of the present application. Suchservices confront similar problems concerning efficient allocation ofcommunication resources between individual base stations (BSs) and themobile stations (MSs) served by an individual BS. Consider the downlinkof a wireless communication system. Here a single BS communicates with aset e.g., plurality, of MSs. The information transmitted to the userscomes with certain delay and rate requirements. For example, voice has aconstant but fairly small rate requirement and fairly stringent delayrequirements. Data traffic e.g., Internet downloads, streaming video,file transfers, on the other hand, have requirements that vary from thetype of traffic and can be very bursty in nature as compared to voicetraffic. Thus, allocating a constant rate channel permanently to a useris usually wasteful in terms of resources. In view of the abovediscussion, there is a need for improved methods and apparatus forallocating bandwidth between users.

SUMMARY

[0004] The present invention is directed to methods and apparatus forenhancing overall throughput in communications systems, e.g., mobilecommunications systems, wherein some flexibility in the scheduling oftransmission times to users corresponding to, e.g., different stations,is possible. Scheduling users when data comes to them results in a moreflexible use of the system resources, e.g., power and bandwidth, thanconstantly allocating them a fixed amount of resource as is generallydone in the cellular telephone where live audio conversations are beingsupported.

[0005] In the present application, communications stations used bysystem users are referred to herein as mobile stations (MS) since theinvention is described in the context of a mobile communications system.However, it is to be understood that the techniques of the presentinvention can be applied where channel conditions may vary. Accordingly,the techniques of the present invention can be applied to both mobile aswell as stationary communications stations.

[0006] In accordance with one embodiment of the present invention a basestation (BS) transmits data to various MSs. The BS decides which MS totransmit to at any given time. Assuming that information, e.g., data,needs to be transmitted to multiple MSs, it is the responsibility of theBS to arbitrate between the needs of the MSs and decide when and for howlong data is to be transmitted to each MS. This process is sometimesreferred to as scheduling, since data is scheduled for transmission tovarious MSs. As part of the scheduling process, the base station mayallocate bandwidth, e.g., a range of frequencies to be used, and theamount of power to be used for transmission purposes.

[0007] The MSs of the present invention provides feedback to the BSregarding channel conditions. In accordance with one feature of thepresent invention, data to be transmitted to MSs is scheduled based onchannel condition feedback information obtained by MSs. When channelconditions are good, data can, and is, transmitted at a higher rate,e.g., bits(s), than when channel conditions are bad. By factoring inchannel condition information, data transmission to MSs is scheduled sothat transmission will occur when an MS is experiencing good channelconditions, e.g., conditions permitting relatively few errors and thushigh transmission rates. In accordance with the present invention,scheduling based on how good a channel each mobile station (MS) has isused to achieve greater overall BS throughput than, e.g., scheduling oftransmissions in a round robin, or a random order independent of MSchannel conditions.

[0008] In order to insure that each user will receive some data evenwhen experiencing poor channel conditions for an extended period oftime, in accordance with various embodiments of the invention thescheduling of data transmission to MSs may take into considerationfactors other than channel conditions alone. For example, when usershave high priority, e.g., because these users have paid more for theservice, and/or if a user's applications have stringent delayrequirements, e.g., as in the case of, streaming video, then the basestation (BS) may schedule users even when their channel is not as goodas desired or when it is worse than another user's channel. Overall BSthroughput may take a hit under such circumstances as compared toembodiments which schedule transmission times solely or primarily basedon channel conditions. This is particularly the case when there arestationary users who do not have a good channel.

[0009] In the case of a non-moving MS or fixed position user station,actual physical channel conditions may remain relatively constant overtime.

[0010] In accordance with one feature of the present invention each BScreates an artificial channel variation, e.g., by transmitting the sameinformation using different transmitters which are physically spacedapart. Assuming two transmitters, e.g., antennas are used, the firsttransmitter broadcasts a first signal with a first information, e.g.,data content, while the second transmitter transmits a second signalwith the same information content but with a different phase and/oramplitude. The difference, e.g., phase and/or amplitude, between thefirst and second signals is varied over time. At the receiver, the firstand second signals interact and are interpreted as a single receivedsignal. The amplitude of the received signal is measured and feed backto the BS as an indication of the channel conditions existing betweenthe BS and MS.

[0011] Thus the BS can schedule the MS as a function of the feedbackinformation including channel state information. As discussed above, thefeedback information is then used as part of a general strategy ofscheduling the user when the channel associated with the user's MSbecomes good enough. This strategy can be used to improve the throughputof the downlink and is efficient even when some MSs are stationary andthus their channels tend not to be naturally changing.

[0012] The strategy of the present invention used in the context of onemobile communications system embodiment is as follows: We have nantennas at the BS and we multiply the signal (which is a complex numberin the base band representation) that is sent to the MSs by complexnumbers, e.g., scaling factors, a₁, . . . , a_(n) and send them on theair over the n antennas. These complex numbers may be, and in at leastone embodiment are, chosen randomly in each time segment data istransmitted. Some desired, but not mandatory, properties of thesecomplex scaling factors a₁, . . . , a_(n) are as follows:

[0013] 1. The sum of magnitude squared of the a_(i) over a period oftime, e.g., symbol period or multiple carrier signal periods, is equalto a constant.

[0014] 2. From time segment to time segment, the complex scaling factorschange in a continuous manner. This makes it easier for the receiver totrack the channel variation and feed back a reliable estimate of thechannel strength.

[0015] The artificial signal variation introduced through the BStransmitting the same information signal from multiple transmitters issomething the BS can track using the channel condition feedbackinformation obtained from the MSs. Accordingly, the BS can use thisvariation, in addition to actual channel variations, to schedule the MSwhen its channel is indicated as being good. As part of the schedulingprocess, in some embodiments, more bandwidth is allocated to MSs whentheir channel conditions are good than when they are poor. In addition,as part of the scheduling process, in some embodiments more power isallocated for transmission to an MS when the MS's channel conditions aregood as opposed to when they are poor.

[0016] In fact, by the strategy described further below, the channel ofthe MS may be twice as good, in terms of the signal to interferenceratio, as compared to the original channel, when the BS schedules an MSin accordance with the present invention.

[0017] In addition to facilitating scheduling of data transmission froma first BS to its MSs, the artificial signal variations of the presentinvention can be beneficial in the case where communications frommultiple BS's overlap, e.g., in the case of overlapping communicationsdomains. In such a case, the signals from one BS appear to another BS aschannel noise. Since the present invention introduces variations intothe signal transmissions between a first BS and an MS, a second, e.g.,neighboring BS, will view the variations as variations in channel noise.Thus the neighboring BS can take advantage of points in time where the“noise” from the first BS is at its minimum to transmit to its own MSs.

[0018] In addition to using channel condition information to scheduletransmission of data from a BS to an MS, channel condition informationcan be used in accordance with the present invention to scheduletransmission of data from an MS to a BS. In one such embodiment, each MSsignals the BS when it has data to upload. The BS arbitrates between thevarious MSs seeking to upload data and schedules the uploads as afunction of the channel conditions existing between the various MSs andBS. In this manner, uploading can be scheduled between various MSs sothat it is performed in an efficient manner.

[0019] Numerous additional features, embodiments, and advantages of thepresent invention are discussed in the detailed description whichfollows.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1A illustrates a communications system including a basestation and a plurality of mobile stations implemented in accordancewith the present invention.

[0021]FIG. 1B illustrates a communications system including several ofthe systems of the type illustrated in FIG. 1 with overlapping broadcastregions.

[0022]FIGS. 2 and 3 illustrate exemplary channel amplitude vs. timeplots.

[0023]FIG. 4 illustrates the communications system of FIG. 1 withvarious feedback signals shown.

[0024]FIG. 5 illustrates a communications system of the presentinvention wherein multiple signals with the same information content aretransmitted from a base station to each mobile station.

[0025]FIG. 6 illustrates a base station implemented in accordance withthe present invention.

[0026]FIG. 7 illustrates a first exemplary mobile station implemented inaccordance with the present invention.

[0027]FIG. 8 illustrates a system of the present invention wherein twolinked base stations operation in conjunction to transmit multiplesignals to each mobile station.

[0028]FIG. 9 illustrates a communications system wherein a plurality ofbase stations and mobile stations are located in the same broadcastregion.

[0029]FIG. 10 illustrates an exemplary mobile station which includesmultiple broadcast antennas implemented in accordance with the presentinvention.

DETAILED DESCRIPTION

[0030] We will begin by describing a very specific example, therebyallowing the invention to first be explained in the context of downlinktransmission using a narrowband frequency range and two antennas at theBS. A more general description of the invention follows this particularexample.

[0031]FIG. 1A shows an example downlink (represented by arrows 110, 112)in a wireless communication system 100. As illustrated, thecommunications system 100 includes a base station 102 and first andsecond mobile stations 104, 106. The basestation (BS) 102 has a fixedlocation and communicates with the first and second mobile stations MS1104 and MS2 106 in some surrounding geographic territory 120 called a“cell” into which BS 102 broadcasts. FIG. 1 shows only the downlink,meaning, the transmissions 110, 112 from the BS to the MSs. In the FIG.1A example, we refer to only two MSs 104, 106. However, the inventioncan be applied to any number N of MSs to which the BS 102 iscommunicating.

[0032] The arrows 110, 112 represent the individual communications links110, 112 from the BS to the MSs 104, 106, respectively. These links willhenceforth also be called channels since they represent communicationspaths or channels over which information can be downloaded to each MS104, 106. These channels may vary with time due to movement of the MSand the scattering environment around the MS, and is also, e.g., tendsto be dependent on the frequency at which the BS 102 communicates withthe MS 104, 106 associated with the channels. Channel conditioninformation is transmitted from MS1 104 and MS2 106 to BS1 and used, inaccordance with the present invention, for scheduling the transmissionof information from BS1 102 to MS1 104 and MS2 106.

[0033] Communications systems of the type illustrated in FIG. 1 may begrouped together to form a larger communications system 150 whichcomprises multiple cells 120, 162, 164 as illustrated in FIG. 1B. In thesystem 150, each cell includes one BS 102, 172, 174 and a plurality ofMSs (not shown). Transmissions from one BS 102, 172, 172 can extend intothe broadcast region of another cell causing signal interference. Areaswhere such interference may occur correspond to the locations wherecells 120, 162 and 164 overlap. As will be discussed below, thisinterference can negatively effect channel conditions for MSs in areaswhere cells overlap.

[0034] Referring once again to the FIG. 1A example, for simplicity, itis assumed that the BS 102 communicates to each MS 104, 106 on onesingle frequency, e.g., f_(k) or over a band that is relatively narrow(1 MHz is relatively narrow enough for most situations) that is centeredat f_(k). This means that the channel may vary in time but is normallyconstant over the frequency range the BS 102 uses to transmit to the MS104 or 106. In FIG. 1A the channel to MS1 is represented by h₁(t) andthe channel to MS2 by h₂(t). The amplitudes of h₁(t) and h₂(t) vary withtime. Exemplary signals h₁(t) associated with MS1 104, and h₂(t)associated with MS2 are shown in FIGS. 2 and 3. Here time t is“slotted”, i.e., we measure time in terms of the number of symbolstransmitted and thus time is indicated using positive integer values.The channel representation is by complex numbers (with real andimaginary parts) and is the so called “base band representation”. Thereal part represents the channel gain when the BS 102 transmits a purecosine waveform at the fixed frequency f_(k) and the imaginary partrepresents the channel gain when the BS 102 transmits a pure sinewaveform at the fixed frequency f_(k). As an example, the BS 102 couldpick the data (denoted by m₁(t), a string of bits 1s and 0s) totransmit. Assuming k=0, the BS 102 modulates this onto the carrier: acomplex tone at frequency f_(o). In such a case, the transmitted signalis

s(t)=m ₁(t)exp(j2πƒ₀ t)

[0035] and the signal received by MS1 104 will be

[0036] s(t)h₁(t)+thermal noise+interference, if any, from other BSs.

[0037]FIG. 4 illustrates the communication system 100 in greater detailwith feedback signals being illustrated. In particular, FIG. 4 will beused to discuss a regime of “coherent reception” at the MS 104 or 106.Coherent reception is used to describe that MS1 104 and MS2 106 tracktheir channels h₁(t) and h₂(t) (relative to the background noise level)respectively, as the channels vary. This is typically achieved by the BS102 transmitting certain symbols called “pilots”, known to the MS 104,106 at known times. The MSs 104, 106 are able to estimate the quality oftheir channels from, e.g., the amplitude and/or phase, of these pilots.The MSs 104, 106 are able to feedback to the BS 102 channel conditioninformation in the form of received signal amplitudes. Such amplitudefeedback information is sometimes called channel “amplitudes”. Thechannel condition information is transmitted to the BS 102 via linkswhich are sometimes called uplinks.

[0038] The MSs 104, 106 can feedback both the amplitude and phase of thechannel over which they are downloading information and thus feedbackthe entire complex channel value. The present invention can be used inembodiments which provide such detailed channel condition information asfeedback.

[0039] However, this may be cumbersome and can cause a heavy load on theuplink used by the MS 104 or 106. Also, there is normally a delay in theprocess of feeding back the channel estimates from the MS 104, 106 tothe BS 102. Thus there is an issue of reliability with regard to channelestimates received by the BS 102. Channel amplitude is usually morerobust than channel phase information. For the above discussed reasons,transmission of channel amplitude information without phase informationis used in the embodiments discussed below.

[0040] Henceforth, we will assume that the timescale of variation of thechannel amplitude is slower than the timescale over which the channelchanges. This is the case in most of the existing wireless communicationsystems. We will assume that the BS 102 has enough data to send to boththe MSs 104, 106. Then the job of the BS 102 is to decide which MS 104or 106 to transmit to, or to transmit to both MSs 104 and 106simultaneously. Below are two exemplary strategies which may beimplemented in accordance with the present invention.

[0041] 1. The BS simply transmits to each MS 104, 106 one at a time, ina roundrobin fashion. The rate at which the BS 102 transmits to the MS104 or 106 is determined by the BS as a function of the channelamplitude strength. In general, larger channel strengths, i.e., achannel with less signal loss, allows for a larger rate of datatransmission than a channel with lower channel amplitude strengthindicative of greater signal loss. Thus, the transmission rate of datato an MS is varied as a function of the quality of the channel whichexists between the MS and the BS.

[0042] 2. A better strategy is to transmit to one MS 104, 106 at a time,but select which MS to transmit to first based on the channel amplitudeassociated with each MS 104, 106. In accordance with the invention, theMS 104 or 106 with the larger channel amplitude indicative of a lowsignal loss, is chosen to be transmitted to first. In addition, the rateat which the BS 102 transmits is determined by the BS as a function ofthe channel amplitude.

[0043] Strategy 2 is likely to provide more downlink throughput thanstrategy 1. The extra gain by using strategy 2 can be quantified and canbe quite large. However, for fairness reasons, as discussed above, theBS 102 may be required to choose an MS 104 or 106 even though it doesnot have the largest channel amplitude. For example, in FIG. 2, theamplitudes of the two channels are more or less symmetrically changing,whereas in FIG. 3, the amplitude of h₂(t) is always below the amplitudeof h₁(t). In an extreme case, one MS 104 or 106 could be stationary, andthus its channel amplitude might not change very much with time. Let usfurther suppose that the channel amplitude of the stationary MS is poorrelative to the other MS's channel amplitude. With strategy 2, thestationary MS, e.g., MS 106, will never be transmitted to. Thus, forfairness reasons, strategy 2 should be modified to allow transmissionsto MSs, e.g., MSs that have not been transmitted to for a given amountof time, even though these MSs may not have the largest channelamplitude. This modification to strategy 2 can make the gain inthroughput over strategy 1 smaller than when channel amplitude is thesole determining factor in selecting an MS 104, 106 to transmit to.

[0044] In accordance with one feature of the present invention discussedbelow, we propose a strategy the BS 102 can use to artificially createvariation in the channel amplitudes of the MSs. This insures variationsin feedback channel amplitudes which can be used to control transmissionscheduling allowing for thereby increased throughput of the downlinkover a pure round-robin allocation system.

[0045]FIG. 5 shows a system 500 including a BS 502 and two MSs 504, 506.FIG. 6 illustrates an exemplary base station 502 in detail.

[0046] As illustrated in FIG. 6, the base station 502 comprises memory602, a processor 614, I/O devices 616 such as a keyboard and displaydevice, a network interface card (NIC) 618, an Internet interface 620,receiver circuitry 622, and transmitter circuitry 624 which are coupledtogether via bus 623. In addition, the base station 502 includes areceiver antenna 630 which is coupled to receiver circuitry 622. Thebase station 502 also includes multiple transmit antennas 632, 634 whichare physically spaced apart from each other. Transmit antennas 632, 634are used for transmitting information to base stations while receiveantenna 630 is used for receiving information, e.g., channel conditionfeedback information as well as data, from MSs.

[0047] The processor 614, under control of routines stored in memory 602is responsible for controlling the overall operation of the base station502. I/O devices 616 are used for displaying system information to abase station administrator and for receiving control and/or managementinput from the administrator. NIC 618 is used for coupling the basestation 502 to a computer network and optionally another base station502. Thus, via NIC 618 base stations may exchange customer informationand other data as well as synchronize the transmission of signals tomobile stations if desired. Internet interface 620 provides a high speedconnection to the Internet allowing MS users to receive and/or transmitinformation over the Internet via the base station 502. Receivercircuitry 622 is responsible for processing signals received viareceiver antenna 630 and extracting from the received signals theinformation content included therein. The extracted information, e.g.,data and channel condition feedback information, is communicated to theprocessor 614 and stored in memory 602 via bus 623. Transmittercircuitry 624 is used to transmit information, e.g., data, and pilotsignals to MSs via multiple antennas, e.g., antennas 632, 634. Aseparate phase/amplitude control circuit 626, 628 is associated witheach of the transmit antennas 632, 634. The antennas 632, 634 at the BS502 are spaced far enough apart so that the signals from the antennas gothrough statistically independent paths and thus the channels thesignals go through are independent of each other. The distance betweenantennas 502, 504 is a function of the angle spread of the MSs, thefrequency of transmission, scattering environment, etc. In general, halfa wavelength separation, based on the transmission frequency, is usuallysufficient. Accordingly, in various embodiments, antennas 502, 504 areseparated by one half a wavelength or more, where a wavelength isdetermined by the carrier frequency f_(k) of the signal beingtransmitted.

[0048] The phase and amplitude control circuits 626, 628 are responsiblefor performing signal modulation and for controlling the phase and/oramplitude of the signal to be transmitted under control of the processor614. Phase/amplitude control circuits 626, 628 introduce amplitudeand/or phase variations into at least one of a plurality, e.g., two,signals being transmitted to an MS to thereby create a variation, e.g.,an amplitude variation over time, in the composite signal received bythe MS to which information is transmitted from multiple antennas. Thecontrol circuits 626, 628 are also capable of varying the datatransmission rate, under control of the processor 614, as a function ofchannel conditions in accordance with the present invention.

[0049] As mentioned above, the processor 614 controls the operation ofthe base station 502 under direction of routines stored in memory 602.The memory 602 includes a transmit schedule/arbitration routine 604, areceiver scheduler/arbitration routine 606, communications routines 612,customer/mobile station data 608 and transmission data 607.

[0050] The transmit scheduler/arbitration routine 604 is responsible forscheduling when data will be transmitted, e.g., downloaded, to MSs. Aspart of the scheduling process routine 604 arbitrates between the needsof various MSs to receive data. The memory 606 also includes a receiverscheduler/arbitration routine 606. The routine 606 is used to schedulewhen MSs will be allowed to upload data to the BS. As with the transmitscheduler 604, the receiver scheduler 606 may arbitrate between severalMSs seeking to upload data at the same time. In accordance with thepresent invention, routines 604, 606 perform scheduling operations as afunction of received channel condition feedback information.Communications routines 612 are used to determine the frequency and datarate as well as the appropriate encoding or modulation technique to beused for communications with each MS. Communications routine 612 canaccess the customer/mobile station data 608 to obtain relevantinformation used by the routines 612. For example, communicationsroutines can access channel condition information 610 obtained fromfeedback to determine the appropriate data rate to be used incommunicating to an MS. In addition, other stored customer information608 can be retrieved and used to determine the appropriate modulationscheme, number of transmission antennas, and transmission frequency tobe used when communicating with a particular MS scheduled to receiveinformation.

[0051] While in some embodiments a single antenna is used to transmitinformation to an MS, the use of multiple physically separated antennas632, 633 allows the same information to be transmitted from differentlocations with controlled phase and/or amplitude differences beingintroduced into at least one of the transmitted signals to produce anartificial signal variance at the receiving MS.

[0052]FIG. 7 illustrates an exemplary mobile station 700 which may beused as any one of the MSs 104, 106. The mobile station 700 includes amemory 702, a processor 714, I/O devices 716, e.g., display, speaker andkeypad, receiver circuit 722 and a transmitter circuit 724 which arecoupled together by a bus 721. A single antenna 730 is coupled to boththe receiver circuit 722 and transmitter circuit 724. However, separatereceiver and transmitter antennas can be used if desired. Memory 702includes several routines as well as data that are used by the processor714 to control the MS 700.

[0053] The memory 702 includes customer/mobile station data 708, achannel condition measurement routine 710, communications routines 712and data to be transmitted, e.g., transmission data 707. Thecommunications routine 712 is responsible for controlling thetransmission and reception of data by circuits 722, 724. Communicationsroutine 712 may vary the data transmission rate, in accordance with thepresent invention based on channel conditions. In addition, it isresponsible to scheduling information received from a BS to insure thatdata is transmitted by the MS at the times authorized by the BS. Channelmeasurement routine 710 is responsible for measuring channel conditionsand supplying amplitude and/or phase feedback information to thecommunications routine 712 which then transmits it to the BS viatransmitter circuit 724. Communications routines 712 are alsoresponsible for controlling the display and/or audio presentation ofreceived information to a MS user via I/O devices 716.

[0054] Referring once again to FIG. 5, it can be seen that the MSs 504,506 each of which has a single receiver antenna, receives a composite ofthe signals broadcast from the two base station antennas 632, 634included in base station 502. FIG. 5 shows the two channels from theantenna pair at the BS 502 to MS1 504 as h₁₁(t) and h₁₂(t) The MSs 504,506 however each have a single antenna 730 and thus the MSs 504, 506receives the composite signal. If the BS 502 transmits s₁(t) and s₂(t)at the two antennas 632, 634, then MS1 504 receives

[0055] h₁₁(t)s₁(t)+h₁₂(t)s₂(t)+thermal noise+interference (if any) fromother BSs

[0056] Consider the following choice of s₁(t) and s₂(t), assuming thatthe BS 502 has chosen the data to be transmitted to MS1 504.

s ₁(t)={square root}{square root over (a_(t)m₁)}(t)exp(j2πƒ₀ t)

s ₂(t)={square root}{square root over (1−a _(t))}m₁(t)exp(j2πδ_(t))exp(j2πƒ

[0057] where

[0058] 1. δ_(t) is a number between 0 and 1 that is randomly chosen foreach time t uniformly between 0 and 1.

[0059] 2. a_(t) is a number between 0 and 1 that is randomly chosen foreach time t uniformly between 0 and 1.

[0060] Observe that the total energy in s₁(t) and s₂(t) is equal to theenergy in m₁(t) which is the same as the earlier case of using a singleantenna. Now consider the case when h₁₁(t) and h₁₂(t) are constant withtime t over which we are interested in communicating. Then the receivedsignal at MS1 504 is

({square root}{square root over (a _(t))}h₁₁+{square root}{square rootover (1−a _(t))}h₁₂exp(j2πδ_(t)))m ₁(t+ interference

[0061] Observe that the amplitude squared of the complex random number(random because a_(t) is random)

({square root}{square root over (a _(t))}h₁₁+{square root}{square rootover (1−a _(t))}h₁₂exp(j2πδ_(t)))

[0062] varies from zero to |h₁₁|²+|h₁₂Å².

[0063] 1. We get zero when a_(t) =|h ₁₂|²/(|h₁₁|²+|h₁₂|²) andδ_(t)=−phase(h₁₁)−phase(h₁₂).

[0064] 2. We get the maximum of |h₁₁|²+|h₁₂|² whena_(t)=h₁₁|²/(|h₁₁|²+|h₁₂|²) and δ_(t)=phase(h₁₁)−phase(h₁₂).

[0065] Thus, we have created an artificial variation of the compositechannel received at the MS 504 and this channel varies in amplitudesquared from 0 to |h₁₁|²+|h₁₂|² randomly in time. If the time scale usedto transmit to MS1 is long enough, then we can limit transmissions toMS1 504 to when MS1's amplitude squared is at or near the largestpossible value—i.e., |h₁₁|²+|h₁₂|² as indicated by the channel conditionfeedback information.

[0066] In practice, it may not be good to vary powers randomly at thetwo antennas (the signals fed to the amplifiers before the antennasnormally should be continuous). We now discuss below some methods ofachieving the effect of artificial channel variation in a continuousmanner in accordance with the present invention.

[0067] 1. We choose a₁=at modulo 1 and δ_(t)=δt modulo 1. The rates aand δ at which the signal powers and phases vary, can be appropriatelychosen. The design criteria for these two rates are: the rates a and δshould be chosen small enough so that the composite channel seen by theMS 504 or 506 does not change too fast and thus, that the feedback ofthe channel amplitude (relative to the interference level) on the uplinkby the MSs 504, 506 to the BS 502 is reliable. Also, we want the ratesto be large enough so that the MSs 504, 506 do not have to wait too longto reach the maximum of their channel variations. Compared to thenonvarying channel case, whenever an MS 504, 506 is scheduled, thechannel should be at least twice as good on the average in terms of thesquared amplitude.

[0068] 2. We could keep a_(t)=0.5 fixed to be constant in time. In thiscase only the phase changes and we can see that the amplitude of thecomposite channel at the MS 504 or 506 now varies from |∥h₁₁|−|h₁₂∥ to|h₁₁|+|h₁₂|.

[0069] 3. The phase rotation itself (represented by δ) can, and invarious embodiments is, introduced using different ones of the followingtechniques:

[0070] (a) Rotate the message symbols m₁(t) themselves by the knownquantity δ_(t) modulo 2π.

[0071] (b) Give the carrier frequency f₀ itself an offset equal to δ.

[0072] With many MSs 504, 506 to which the BS 502 is communicating with,at any point in time, it will be very likely the case that there is atleast one MS 504 or 506 for which the current choice of a_(t) and δ_(t)are such as to give the maximum amplitude squared of its channel. Thenthe BS 502 can simply decide to transmit to only this MS 504 or 506. Thefeedback required at the BS 502 from each MS 502, 504 is the compositechannel amplitude detected by the MS 504, 506. Thus, the strategydescribed here applies equally well to the situation when there are morethan two MSs. In fact, the more MSs, the more flexible the schedule atthe BS 502 is, and thus the throughput tends to increase by using thisstrategy. Accordingly, the methods of the present invention can beapplied to a system including N MSs, where N is a positive integer equalto or greater than two.

[0073] While we have discussed the present invention in terms ofbroadcasting using two antennas coupled to a single base station, thebroadcasting may actually be performed by two linked base stations 704,706 which broadcast into the same geographic region 712 as illustratedin FIG. 8. In the FIG. 8 embodiment, BS1 704 receives channel feedbackinformation and schedules transmissions to the MSs 708, 710. However,rather than use two antennas at BS1 704, a first signal is transmittedfrom BS1 and a second signal with the same information content but witha different phase and/or amplitude, is transmitted from BS2 706. NICs618 included in each BS 704, 706 may be used to couple the base stations704, 706 together via a network connection so that transmission andcontrol functions can be coordinated between the two base stations 704,706.

[0074]FIG. 9 shows the transmission between a BS 902 and many MSs 904,906, 908, 910 in a geographic region 901 with N base stations 902, 916.Thus, in the system 900, given that there are multiple base stations inthe same broadcast region, signal interference from neighboring basestations will be present. We have symbolically represented the linksfrom the BS 102 to the MSs by h₁, . . . , h_(n) and the feedback fromthe MSs to the BS 902 by g₁, . . . , g_(n). Each link h₁, . . . , h_(n)may correspond to multiple independent signal paths, from separateantennas, which provide signals to each MS which are interpreted as asingle composite signal. In the previous specific example, the readerwas given examples of what the feedback signals could be, e.g., channelamplitude and/or phase information. However, the feedback signals neednot be limited to just those specific exemplary quantities. The feedbackquantities g₁, . . , g_(n) give information to the BS 902 about thequality of the channel, e.g., an estimate of the rate and power at whichthe MSs 904, 906, 908, 910 can receive transmission from the BS 902reliably.

[0075] One scheme to change the channel variation and use the resultingordering of transmission channels based on quality for purposes ofordering transmissions to MS users is as follows:

[0076] 1.Take the signal (in baseband) to be transmitted and multiply itby complex numbers a₁, . . . , a_(n). These complex numbers aregenerated randomly each time or made to vary slowly over time asdescribed above. Two desirable properties for scaling factors is that:

[0077] (a) the sum of the magnitude squared of the scaling factors beconstant to maintain the same total transmission power at the BS 902;and

[0078] (b) the scaling factors vary over their entire possible range ina continuous manner.

[0079] 2. Use the feedback g₁, . . . , g_(n) from the MSs 904, 906, 908,910 to decide which order to transmit signals to MSs and thus, users ofthe MSs. Several scheduling policies can be used here, however, the MSswhich have good channel conditions are normally favored over those withbad channel conditions. The overall scheduling policy can includepriorities of the users, fairness to users, and other such conditions.In addition, transmission rates to the MSs may be determined based onthe feedback information.

[0080] The bottom line is that by making the channel variation happen bythe antenna scheme discussed above, even where there is no physicalvariation in channel conditions, our scheme coupled with the ordering ofthe transmission to the users based on the feedback from them allowsgain in throughput of the wireless communication system due to reducedinterference from neighboring BSs.

[0081] In the case where an MS can potentially communicate with multipleBSs, e.g., due to overlapping coverage as in the FIG. 9 illustration,the above described scheme can, and in some embodiments is, applied onthe uplink as well where uplink is the communication from an MS to a BS.In one such case, an MS 904, 906, 908, 910 selects the BS 902 or 916,from a plurality of possible BSs, to transmit to based on channelcondition information with the channels with good conditions beingpreferred over channels with bad or worse conditions.

[0082] The methods and apparatus of the present invention can be appliedto other scenarios including those discussed below.

[0083] The scheduling and rate control techniques of the presentinvention can be used to schedule and control uplink transmissions tothe BS. In such a case, multiple antennas will be used at each of theMSs. FIG. 10 illustrates an MS 1000 which is similar to the previouslydescribed MS 700 but includes multiple transmit circuits 1024, 1026 andtransmit antennas 1030, 1032 in accordance with the present invention.As in the case of a BS implemented in accordance with the presentinvention, transmit antennas 1030, 1032 are spaced apart so theirsignals travel to a BS over different paths while the transmittercircuits are used to introduce phase and/or amplitude variations intothe signals being transmitted by the two antennas 1030, 1032. In such anembodiment the BS measures the channel condition, e.g., from pilotstransmitted by each MS, and then decides which MS to schedule based onthis information. A difference from the downlink scheme described aboveis that there is no need for feedback of the channel state information.This is because the BS itself estimates the uplink channel condition andschedules the MSs using a scheduling algorithm that favors the MSs whosechannel states are good over those with poor channel statistics. Uplinktransmit schedule information is transmitted from the BS to the MSs sothat they know when, and at what rate, to transmit information to theBS.

[0084] It should be noted that the scheduling and data rate controltechniques described above for use with downlinks and uplinks areapplicable in cellular environments wherein multiple potentiallyoverlapping cells exist. Given bandwidth reuse among cells, the linkfrom the BS to the MS may be characterized by two quantities in acellular environment: the quality of the channel from the BS to the MSand the interference caused by transmissions in other cells. Both thesequantities go through the same type of fluctuations under the schemedescribed above and the BS can schedule transmissions to and from thoseMSs which have both good channel conditions and limited interferencefrom other cells as well as control the rate of uplink and/or downlinktransmissions.

[0085] The methods and apparatus of the present invention are applicableto a wide range of Multiple Access techniques. In the description above,we have recognized that a great deal of flexibility exists in how theresources, particularly bandwidth and time, are split among the MSs andthus various users.

[0086] We will now discuss various exemplary splits in resources whichcan be applied in various cases. Numerous additional possibilitiesexist. For purposes of brevity we will limit the following discussion toexamples applied to the downlink with the understanding that the same orsimilar resource allocation techniques can be applied to uplinks aswell.

[0087] (a) TDMA: In this case, time is slotted and only one MS istransmitted to from the BS. In this case, the schedule policy used bythe BS can be to simply decide which MS to transmit to at any slot oftime.

[0088] (b) FDMA: The application of our scheme is a bit more involved inthis case. Now feedback is used from the MS regarding the quality of thechannel in each of the frequency slots. Then the BS can schedule the MSsto those frequency slots where the MS has the best channel condition.

[0089] (c) CDMA: Under the restriction that users with orthogonal oralmost orthogonal codes only are allowed to be transmitted to, thescheme described above applies directly. In particular, if one MS istransmitted to, then the applicability is direct.

[0090] (d) OFDM: This scenario is very similar to FDMA. Here thefrequency slots are “logical”, in the sense that each slot is actually aparticular hopping sequence. However, the hopping sequences arenonoverlapping in time and thus the equivalence to FDMA from the pointof view of orthogonality of the different slots.

[0091] Numerous addition embodiments and variations of the abovedescribed methods and apparatus will be apparent to those skilled in theart in view of the above description of the present invention. Suchmethods and apparatus are to be considered within the inventiondescribed herein.

What is claimed is:
 1. A communications method for use in acommunications system including a first device and a second device, themethod comprising the steps of: operating the first device to receivefirst communications channel condition information regarding thecondition of a first communications channel existing between the firstdevice and the second device; and determining, as a function of thefirst communications channel condition information, when to transmitdata from the first device to said second device.
 2. The communicationsmethod of claim 1, further comprising the step of: determining the rateat which to transmit data to the first device as a function of the firstcommunications channel condition information.
 3. The communicationsmethod of claim 2, further comprising the step of: allocating bandwidthas a function of the determined data transmission rate.
 4. Thecommunications method of claim 3, wherein the step of allocatingbandwidth includes: allocating a first amount of bandwidth when thedetermined data transmission rate is a first rate; and allocating asecond amount of bandwidth which is greater than the first amount whenthe determined data transmission rate is a second rate which is greaterthan the first rate.
 5. The communications method of claim 2, furthercomprising the step of: controlling the amount of power used to transmitdata from the first device to the second device as a function of thedetermined data transmission rate.
 6. The communications method of claim2, further comprising: using a first amount of power to transmit datafrom the first device to the second device when the determined datatransmission rate is a first rate; and using a second amount of power totransmit data from the first device to the second device, which isgreater than the first amount of power, when the determined datatransmission rate is a second rate which is greater than the first rate.7. The method of claim 1, wherein the system further includes a thirddevice, the method further comprising: operating the first device toreceive second communications channel condition information regardingthe condition of a second communications channel existing between thefirst device and the third device; and determining, as a function of thesecond communications channel condition information, when to transmitdata to said third device.
 8. The method of claim 7, further comprisingthe step of: operating the second device to measure the amplitude of afirst signal received from the first device; and transmitting firstsignal amplitude information from the second device to the first device,said first communications channel condition information including saidfirst signal amplitude information.
 9. The method of claim 8, furthercomprising the step of: operating the third device to measure theamplitude of a second signal received from the first device; andtransmitting second signal amplitude information from the third deviceto the first device, said second communications channel conditioninformation including said second signal amplitude information.
 10. Themethod of claim 9, wherein the first device is a base station, and thesecond and third devices are mobile stations.
 11. The method of claim 7,wherein the step of determining when to transmit data includes the stepof: scheduling data transmissions to said second and third devices suchthat the devices associated with better channel conditions are givenscheduling preference over devices associated with poorer channelconditions.
 12. The method of claim 7, further comprising the steps of:transmitting a first data signal from the first device to the seconddevice, the step of transmitting including: introducing a variation intothe first data signal which can be detected by the second device as achange in the first data signal over time.
 13. The method of claim 12,wherein the variation introduced into the first data signal includes atleast one of a phase variation and an amplitude variation.
 14. Themethod of claim 12, wherein said first data signal includes a pilotsignal.
 15. The method of claim 14, wherein said introduced variation isa phase variation.
 16. The method of claim 14, wherein said introducedvariation is an amplitude variation.
 17. The method of claim 7, furthercomprising the steps of: transmitting, using a plurality of N antennas,the same data to the second device, N being a positive integer greaterthan one, the step of transmitting including: transmitting from a firstantenna in said plurality of N antennas a first data signal includingsaid data; and transmitting from a second antenna in said plurality of Nantennas a second data signal including the same data as said first datasignal, the second data signal having a phase which is different fromthe first data signal.
 18. The method of claim 17, further comprisingthe step of: varying the phase of at least one of the first and seconddata signals being transmitted as a function of time.
 19. The method ofclaim 18, wherein the first and second data signals have the same centerfrequency, fc.
 20. The method of claim 19, further comprising the stepof spacing the first and second antennas at least one half a wavelengthapart, wherein the wavelength is equal to C divided by fc, where C isthe speed of light.
 21. The method of claim 17, wherein the first andsecond data signals have the same carrier frequency, fc.
 22. The methodof claim 20, further comprising the step of spacing the first and secondantennas at least one half a wavelength apart, wherein the wavelength isequal to C divided by fc, where C is the speed of light.
 23. The methodof claim 18, further comprising the step of: varying the relativeamplitudes of the first and second data signals over time.
 24. Themethod of claim 23, wherein the first and second data signal includesymbols having a symbol period, the method further comprising the stepof: using a fixed average amount of power over at least one symbolperiod to transmit the combination of the first and second data signals.25. The method of claim 17, further comprising the step of: varying therelative amplitudes of the first and second data signals as a functionof time while maintaining the combined average transmitted power of thefirst and second data signals at an almost constant value over theperiod in time during which the relative amplitudes of the first andsecond data signals are varied.
 26. The method of claim 25, wherein N isgreater than two.
 27. A communications method, comprising the steps of:operating a base station to receive channel condition information fromeach of a plurality of mobile stations, the channel conditioninformation received from each mobile station including informationindicating the quality of a communications channel associated with themobile station; and scheduling transmissions to said mobile stationsfrom said base station as a function of the quality of thecommunications channel associated with the individual mobile stations.28. The communications method of claim 27, further comprising the stepof: allocating bandwidth for data transmissions to said mobile stationsfrom said base stations as a function of the quality of thecommunications channel associated with the individual mobile stations.29. The communications method of claim 28, wherein the step ofallocating bandwidth includes: allocating more bandwidth when thequality of the communications channel associated with an individualmobile station is in a first state than when the communications channelassociated with an individual mobile station is in a second state whichis poorer for communications than the first state.
 30. Thecommunications method of claim 27, further comprising the step of:controlling the amount of power used to transmit data from the basestation to one of the mobile stations as a function of the quality ofthe communications channel associated with said one of the mobilestations.
 31. The communications method of claim 30, wherein the step ofcontrolling the amount of power includes the step of: using a firstamount of power to transmit data from the base station to said one ofthe mobile stations when the quality of the communications channelassociated with said one of the mobile stations is of a first degree ofquality; and using a second amount of power to transmit data from thefirst device to the second device, which is greater than the firstamount of power, when the quality of the communications channelassociated with said one of the mobile stations is of a second degree ofquality which is better for communications than the first degree ofquality.
 32. The communications method of claim 27, further comprisingthe step of: determining the rate at which to transmit data to each ofsaid mobile stations as a function of the quality of the communicationschannel associated with each of the mobile stations.
 33. Thecommunication method of claim 27, wherein the step of schedulingtransmission to said mobile stations includes the step of: operating ascheduling routine which includes a preference for transmitting tomobile stations associated with communications channels having goodchannel conditions prior to transmitting to mobile stations associatedwith communications channels with poorer channel conditions.
 34. Thecommunications method of claim 33, further comprising the step of:transmitting first and second signals including the same information toeach mobile station, the step of transmitting including: using a firstantenna to transmit the first signal; and using a second antenna totransmit the second signal.
 35. The communications method of claim 34,wherein the first and second signals vary in relation to one anotherover time in at least one of phase and amplitude but have the samecenter frequency.
 36. The communications method of claim 34, wherein thefirst and second signals vary in relation to one another over time in atleast one of phase and amplitude but have the same carrier frequency.37. The communications method of claim 34, wherein the second antenna islocated at a second base station, the method further comprising the stepof: operating the first base station to control the second base stationto broadcast the second signal using the second antenna located at thesecond base station.
 38. The communications method of claim 37, furthercomprising the step of: determining the rate at which to transmit datato each of said mobile stations as a function of the received channelcondition information.
 39. A communications method, comprising the stepsof: operating a base station to estimate the condition of communicationschannels between the base station and mobile stations from signalsreceived from the mobile stations; and scheduling transmissions fromsaid mobile stations to said base station as a function of the estimatedquality of the communications channels between the individual mobilestations and the base station.
 40. The communications method of claim39, further comprising the step of: determining the rate at which totransmit data to at least one of said mobile stations as a function ofthe estimated channel condition information.
 41. The communicationsmethod of claim 40, further comprising the step of: allocating bandwidthfor communications to the at least one of said mobile stations as afunction of the determined data transmission rate.
 42. Thecommunications method of claim 40, further comprising the step of:controlling the amount of power used to transmit data to the at leastone of said mobile stations as a function of the determined datatransmission rate.
 43. The communication method of claim 40, wherein thestep of scheduling transmission to said mobile stations includes thestep of: operating a scheduling routine which includes a preference forallowing mobile stations associated with communications channels havinggood channel conditions to transmit prior to mobile stations associatedwith communications channels with poorer channel conditions.
 44. Amethod of transmitting data between a first device and a second device,comprising the steps of: providing a plurality of N separate antennas,said plurality including at least a first antenna and a second antenna,N being a positive integer greater than one; operating the first deviceto transmit from the first antenna, a first signal including said datathe first signal having a carrier frequency, fc, a broadcast region fromthe first antenna including the second device; operating the firstdevice to transmit from the second antenna, a second signal includingsaid data the second signal having the same carrier frequency, fc, asthe first signal, a broadcast region from the second antenna includingthe second device, at least one of a phase and an amplitude of thesecond signal varying over time relative to the first signal.
 45. Themethod of claim 44, wherein the phase of the second signal varies overtime relative to the phase of the first signal, the method furthercomprising the step of: introducing a variation into the phase of thesecond signal as a function of time prior to operating the secondantenna to transmit the second signal.
 46. The method of claim 45,further comprising the step of: controlling the rate at which data istransmitted as part of the first signal as a function of transmissionchannel quality information.
 47. The method of claim 45, wherein thefirst device is a base station and the second device is a mobilestation.
 48. The method of claim 45, wherein the first device is amobile station and the second device is a base station.
 49. A method oftransmitting data between a first device and a second device, comprisingthe steps of: providing a plurality of N separate antennas, saidplurality including at least a first antenna and a second antenna, Nbeing a positive integer greater than one; operating the first device totransmit from the first antenna, a first signal including said data thefirst signal having a center frequency, a broadcast region from thefirst antenna including the second device; operating the first device totransmit from the second antenna, a second signal including said datathe second signal having the same center frequency as the first signal,a broadcast region from the second antenna including the second device,at least one of a phase and an amplitude of the second signal varyingover time relative to the first signal.
 50. The method of claim 49,further comprising the steps of: introducing a variation into the phaseof the second signal as a function of time prior to operating the secondantenna to transmit the second signal; and controlling the rate at whichdata is transmitted as part of the first signal as a function oftransmission channel quality information.
 51. A communicationsapparatus, comprising: a source of data; a transmitter circuit coupledto the source of data for generating a plurality of data signals eachdata signal including the same data, the plurality of data signalsincluding a first data signal and a second data signal the first andsecond data signals differing from one another as a function of time byat least one of a phase and an amplitude; and a plurality of antennascoupled to said transmitter circuit to receive and transmit said datasignals in parallel, each antenna receiving and transmitting one of saiddata signals.
 52. The apparatus of claim 51, wherein the transmittercircuit includes means for independently varying the phase of at leastone of the first and second data signals as a function of time.
 53. Theapparatus of claim 52, further comprising: a receiver for receivingcommunications channel condition information; and means for determiningthe rate at which data should be transmitted in said first and seconddata signals as a function of the communications channel information.54. The apparatus of claim 52, further comprising: a receiver forreceiving communications channel condition information from a pluralityof mobile stations regarding the condition of a communications channelassociated with individual ones of said plurality of mobile stations;and means for scheduling transmission of data to individual mobilestations as a function of the received communications channel conditioninformation.
 55. The apparatus of claim 54, wherein the means forscheduling includes a scheduling routine which gives preferentialtreatment to the scheduling of data transmissions to mobile stationswith good communications channels as compared to mobile stations withpoorer communications channels.
 56. The apparatus of claim 55, furthercomprising: means for determining the rate at which data should betransmitted in said first and second data signals as a function of thecommunications channel information.
 57. The apparatus of claim 54,wherein the first and second data signals have the same centerfrequency, fc and a wavelength W at the center frequency; and whereinthe first and second antennas are spaced at least one half the distanceof the wavelength W from each other.
 58. The apparatus of claim 54,wherein the first and second data signals have the same carrierfrequency, fc and a wavelength W at the carrier frequency; and whereinthe first and second antennas are spaced at least one half the distanceof the wavelength W from each other.
 59. The apparatus of claim 51,wherein the first and second data signals have the same centerfrequency, fc and a wavelenth W at the center frequency; and wherein thefirst and second antennas are spaced at least one half the distance ofthe wavelenth W from each other.
 60. The apparatus of claim 51, whereinthe first and second data signals have the same carrier frequency, fcand a wavelenth W at the carrier frequency; and wherein the first andsecond antennas are spaced at least one half the distance of thewavelenth W from each other.
 61. The apparatus of claim 51, furthercomprising: means for using a fixed amount of power to transmit thecombination of the first and second data signals over time.
 62. Theapparatus of claim 61, further comprising: means for varying therelative amplitudes of the first and second data signals as a functionof time while maintaining the combined average transmitted power of thefirst and second data signals at an almost constant value over theperiod in time during which the relative amplitudes of the first andsecond data signals are varied.
 63. A communications system, comprising:a mobile station; and a base station, the base station including: i. areceiver for receiving communications channel condition informationregarding the condition of a first communications channel existingbetween the first device; and ii. means for determining the rate atwhich data is transmitted to said mobile station as a function of thechannel condition information.
 64. The communications system of claim63, further comprising: a plurality of additional mobile stations, thebase station receiver receiving additional communications channelcondition information regarding the condition of additionalcommunications channels existing between the base station and saidadditional mobile stations.
 65. The communication system of claim 64,further comprising: means for determining the order in which the basestation is to transmit data to different mobile stations as a functionof said communication channel condition information and said additionalcommunications channel condition information.
 66. The communicationsystem of claim 65, wherein the base station further includes: at leasta first and second antenna for broadcasting first and second signalsincluding the same data to one of said mobile stations, the first andsecond signals having different phases.
 67. The communication system ofclaim 65, wherein the base station further includes: at least a firstand second antenna for broadcasting first and second signals includingthe same data to one of said mobile stations the first and secondsignals having different amplitudes.
 68. The communication system ofclaim 65, wherein the base station further includes: means forintroducing signal variations into signals transmitted to the mobilestations so that the mobile stations will detect fluctuations inreceived signal power.
 69. The communication system of claim 68, whereinsaid means for introducing signal variations into signals includes aplurality of antennas for transmitting the same data in parallel.
 70. Amobile communications device, comprising: a portable housing;transmitter circuitry, mounted in said portable housing, for generatinga plurality of signals including the same data content but having phaseswhich vary relative to each other over time; and a plurality of antennasattached to said housing, said antennas being coupled to saidtransmitter circuitry, each antenna being used to transmit a differentone of said plurality of signals including the same data content. 71.The device of claim 70, further comprising: receiver circuitry forreceiving a signal from a base station; and means for generatingcommunications channel condition information from the signal receivedfrom the base station.